A fluid flow conveyed through a flow channel is regularly deflected by a lateral pressure gradient parallel to the side walls. Due to the lower velocity thereof, the flow layers proximal to the wall are deflected to a greater degree than the flow layers distal to the wall, thereby forming a secondary flow that is superimposed on a primary flow. This leads to vortices and, inter alia, to pressure losses. The secondary flows regularly occur in blade cascades of turbomachines, such as gas and steam turbines. The blade cascades are composed of a multiplicity of blades or airfoils, which are adjacently disposed in the circumferential direction of the turbomachine and disposed in a rotationally-symmetric flow channel, what is commonly known as an annulus, and between each of which, a blade channel is formed in which the secondary flows are formed. In the circumferential direction of the turbomachine, the blade channels are each delimited by a pressure side and a suction side of the mutually adjacent blades. In the radial direction of the turbomachine, the blade channels are each delimited by a radially outer, respectively housing-side side wall and by a radially inner, respectively hub-side side wall. The side walls are formed by a stationary housing section, by a rotor section, by radially inner shroud plates and/or by radially outer shroud plates. To reduce the secondary flows, contours in the form of elevations and/or depressions are frequently introduced into the side walls.
From the related art, a multiplicity of what are generally referred to as side-wall contours are known. Mentioned exemplarily are the patents or patent applications of the Applicant EP 2 487 329 B1, EP 2 787 172 A2, and EP 2 696 029 B1.